Magnetoresistance Element with Improved Response to Magnetic Fields

ABSTRACT

A magnetoresistance element has a pinning arrangement with two antiferromagnetic pinning layers, two pinned layers, and a free layer. A spacer layer between one of the two antiferromagnetic pinning layers and the free layer has a material selected to allow a controllable partial pinning by the one of the two antiferromagnetic pinning layers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of and claims priority toand the benefit of U.S. patent application Ser. No. 14/529,564, filedOct. 31, 2014, which claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application No. 61/925,446 filed Jan. 9, 2014, whichapplications are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD

This invention relates generally to spin electronics magnetoresistanceelements and, more particularly, to giant magnetoresistance (GMR)elements and tunnel magnetoresistance (TMR) elements that have animproved response to magnetic fields.

BACKGROUND

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. One such magnetic field sensing element is a magnetoresistance(MR) element. The magnetoresistance element has a resistance thatchanges in relation to a magnetic field experienced by themagnetoresistance element.

As is known, there are different types of magnetoresistance elements,for example, a semiconductor magnetoresistance element such as IndiumAntimonide (InSb), a giant magnetoresistance (GMR) element, ananisotropic magnetoresistance element (AMR), and a tunnelingmagnetoresistance (TMR) element, also called a magnetic tunnel junction(MTJ) element.

Of these magnetoresistance elements, the GMR and the TMR elementsoperate with spin electronics (i.e., electron spins) where theresistance is related to the magnetic orientation of different magneticlayers separated by nonmagnetic layers. In spin valve configurations,the resistance is related to an angular direction of a magnetization ina so-called “free-layer” respective to another layer so-called“reference layer.” The free layer and the reference layer are describedmore fully below.

The magnetoresistance element may be a single element or, alternatively,may include two or more magnetoresistance elements arranged in variousconfigurations, e.g., a half bridge or full (Wheatstone) bridge.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. In a typical magnetic field sensor, themagnetic field sensing element and the other circuits can be integratedupon a common substrate.

Magnetic field sensors are used in a variety of applications, including,but not limited to, an angle sensor that senses an angle of a directionof a magnetic field, a current sensor that senses a magnetic fieldgenerated by a current carried by a current-carrying conductor, amagnetic switch that senses the proximity of a ferromagnetic object, arotation detector that senses passing ferromagnetic articles, forexample, magnetic domains of a ring magnet or a ferromagnetic target(e.g., gear teeth) where the magnetic field sensor is used incombination with a back-biased or other magnet, and a magnetic fieldsensor that senses a magnetic field density of a magnetic field.

Various parameters characterize the performance of magnetic fieldsensors and magnetic field sensing elements. With regard to magneticfield sensing elements, the parameters include sensitivity, which is thechange in the output signal of a magnetic field sensing element inresponse to a magnetic field, and linearity, which is the degree towhich the output signal of a magnetic field sensor varies linearly(i.e., in direct proportion) to the magnetic field.

GMR and TMR elements are known to have a relatively high sensitivity,compared, for example, to Hall elements. GMR and TMR elements are alsoknown to have moderately good linearity, but over a restricted range ofmagnetic fields, more restricted in range than a range over which a Hallelement can operate. However, it is known that even in the restrictedrange of magnetic fields, the linearity of the GMR or TMR elementsuffers from irregularities. Also, it is known that some GMR and TMRelements tend to change behavior after high temperature storage. Thus,it would be desirable to provide a GMR or a TMR element for whichlinearity irregularities are reduced and for which high temperaturestorage has a reduced effect.

Conventional GMR and TMR elements, and, in particular, spin valves, areknown to also have an undesirable hysteresis behavior, which reducestheir accuracy of magnetic field or current measurements. Thus, it wouldalso be desirable to provide a GMR or TMR element with reducedhysteresis.

SUMMARY

The present invention provides a GMR or a TMR element (or any spinelectronics magnetoresistance element) for which linearityirregularities are reduced, hysteresis behavior is strongly reduced, andfor which high temperature and high field storage conditions have areduced effect.

In accordance with an example useful for understanding an aspect of thepresent invention, a magnetoresistance element includes a firstsynthetic antiferromagnet (SAF) structure, comprising: a firstferromagnetic layer; a second ferromagnetic layer; and a spacer layerbetween the first and second ferromagnetic layers, wherein the spacerlayer is comprised of a selected material with a selected thickness toallow an antiferromagnetic coupling between the first and secondferromagnetic layers. The magnetoresistance element further includes asecond synthetic antiferromagnet (SAF) structure, comprising: a firstferromagnetic layer; a second ferromagnetic layer; and a spacer layerbetween the first and second ferromagnetic layers, wherein the spacerlayer is comprised of a selected material with a selected thickness toallow an antiferromagnetic coupling between the first and secondferromagnetic layers. The magnetoresistance element further includes afirst antiferromagnetic layer disposed proximate and coupled to thefirst synthetic antiferromagnet (SAF) structure and a secondantiferromagnetic layer disposed proximate and coupled to the secondsynthetic antiferromagnet (SAF) structure, such that the first andsecond synthetic antiferromagnet (SAF) structures are disposed betweenthe first and second antiferromagnetic layers. The magnetoresistanceelement further includes a free layer structure disposed between thefirst and second synthetic antiferromagnet (SAF) structures. Themagnetoresistance element further includes a first nonmagnetic layerdisposed between the first synthetic antiferromagnet (SAF) structure andthe free layer structure and a second nonmagnetic layer disposed betweenthe second synthetic antiferromagnet (SAF) structure and the free layerstructure. A material of the first nonmagnetic layer is selected toallow a thickness of the first nonmagnetic layer to be greater than 0.5nm while allowing a desired partial pinning between the first syntheticantiferromagnet (SAF) structure and the free layer structure.

In accordance with another example useful for understanding an aspect ofthe present invention, a method of fabricating a magnetoresistanceelement includes depositing a magnetoresistance element upon asubstrate, the magnetoresistance element including a first syntheticantiferromagnet (SAF) structure, comprising: a first ferromagneticlayer; a second ferromagnetic layer; and a spacer layer disposed betweenthe first and second ferromagnetic layers, wherein the spacer layer iscomprised of a selected material with a selected thickness to allow anantiferromagnetic coupling between the first and second ferromagneticlayers. The magnetoresistance element further includes a secondsynthetic antiferromagnet (SAF) structure, comprising: a firstferromagnetic layer; a second ferromagnetic layer; and a spacer layerdisposed between the first and second ferromagnetic layers, wherein thespacer layer is comprised of a selected material with a selectedthickness to allow an antiferromagnetic coupling between the first andsecond ferromagnetic layers. The magnetoresistance element furtherincludes a first antiferromagnetic layer disposed proximate to andcoupled to the first synthetic antiferromagnet (SAF) structure and asecond antiferromagnetic layer disposed proximate to and coupled to thesecond synthetic antiferromagnet (SAF) structure, such that the firstand second synthetic antiferromagnet (SAF) structures are disposedbetween the first and second antiferromagnetic layers. Themagnetoresistance element further includes a free layer structuredisposed between the first and second synthetic antiferromagnet (SAF)structures. The magnetoresistance element further includes a firstnonmagnetic layer disposed between the first synthetic antiferromagnet(SAF) structure and the free layer structure and a second nonmagneticlayer disposed between the second synthetic antiferromagnet (SAF)structure and the free layer structure. A material of the firstnonmagnetic layer is selected to allow a thickness of the firstnonmagnetic layer to be greater than 0.5 nm while allowing a desiredpartial pinning between the first synthetic antiferromagnet (SAF)structure and the free layer structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a graph showing an ideal and an actual transfer characteristicof a giant magnetoresistance (GMR) element;

FIG. 2 is a block diagram showing layers of a conventional prior art GMRelement with a single pinned arrangement;

FIG. 3 is a block diagram showing layers of a conventional prior art GMRelement with a double pinned arrangement;

FIG. 4 is a block diagram showing layers of an example of amagnetoresistance element having a particular double pinned arrangement;

FIG. 5 is a top view diagram of magnetic field sensing element having ayoke shape that, in some embodiments, can describe a shape of themagnetoresistance element of FIG. 4, 10, or 11;

FIG. 6 is a block diagram of a magnetoresistance element magnetic fieldsensor placed above a magnetic target for rotation speed measurement;and

FIG. 7 is a flow chart showing an example of process steps that can beused to form the double pinned GMR element of FIGS. 4, 5, 10, and 11;

FIGS. 8 and 9 are flow charts showing examples of alternate processsteps that can be used to form the double pinned GMR element of FIGS. 4,5, 10, and 11,

FIG. 10 is a block diagram showing layers of another example of amagnetoresistance element having a particular double pinned arrangement;and

FIG. 11 is a block showing layers of yet another example of amagnetoresistance element having a particular double pinned arrangement.

DETAILED DESCRIPTION

Before describing the present invention, it should be noted thatreference is sometimes made herein to GMR or TMR elements havingparticular shapes (e.g., yoke shaped). One of ordinary skill in the artwill appreciate, however, that the techniques described herein areapplicable to a variety of sizes and shapes.

As used herein, the term “anisotropy” or “anisotropic” refer to aparticular axis or direction to which the magnetization of aferromagnetic or ferrimagnetic layer tends to orientate when it does notexperience an additional external field. An axial anisotropy can becreated by a crystalline effect or by a shape anisotropy, both of whichallow two equivalent directions of magnetic fields. A directionalanisotropy can also be created in an adjacent layer, for example, by anantiferromagnetic layer, which allows only a single magnetic fielddirection along a specific axis in the adjacent layer.

In view of the above, it will be understood that introduction of ananisotropy in a magnetic layer results in forcing the magnetization ofthe magnetic layer to be aligned along that anisotropy in the absence ofan external field. In case of a GMR or TMR element, a directionalanisotropy provides an ability to obtain a coherent rotation of themagnetic field in a magnetic layer in response, for example, to anexternal magnetic field, which has the property of suppressing thehysteresis behavior of the corresponding element.

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. A magnetoresistance element is but one type of magnetic fieldsensing elements.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnet,and a magnetic field sensor that senses a magnetic field density of amagnetic field.

Structures and methods described herein apply to both GMR and TMRmagnetoresistance elements. However, it should be appreciated that thesame or similar structures and methods can apply to other spinelectronics magnetoresistance elements, either now known or laterdiscovered. This includes in particular oxide based spin electronicsstructures.

Referring now to FIG. 1, a graph 100 has a horizontal axis with a scalein units of magnetic field in milliTesla (mT) and a vertical axis with ascale in units of resistance in arbitrary units.

A curve 102 is representative of a transfer function of an ideal GMRelement, i.e., resistance versus magnetic field experienced by the GMRelement. The transfer function 102 has a linear region 102 a between anupper saturation point 102 b and a lower saturation point 102 c. Regions102 d, 102 e are in saturation. It should be understood that the linearregion 102 a is an ideal linear region. Furthermore an ideal GMR elementpresents the same value of resistance for a given field independently ofits magnetic history.

Steps, e.g., a step 104, are representative of an actual transferfunction of the GMR element. Beyond the saturation points 102 b, 102 c,the actual transfer function represented by the steps 104 merges withthe saturation regions 102 d, 102 e.

The steps 104 are not desirable. The steps 104 result from magneticbehavior of magnetic domains within a so-called free layer in a GMRelement. Behavior of the free layer is described more fully below inconjunction with FIG. 2.

While the steps 104 are shown to be regular steps with equal spacing andequal step heights, the steps 104 can also be irregular, with unequalspacing and unequal step heights (i.e., amplitudes). The steps usuallycorrespond to local hysteretic and on reproducible local rotation of thefree layer.

Referring now to FIG. 2, a conventional prior art GMR element 200includes a plurality of layers disposed over a substrate. An uppersurface of the substrate is shown as a lowermost line at the bottom ofFIG. 2.

On the left side of FIG. 2, each layer is identified by functional name.On the right side or FIG. 2 are shown magnetic characteristics ofsub-layers that can form the functional layers. In general, magneticmaterials can have a variety of magnetic characteristics and can beclassified by a variety of terms, including, but not limited to,ferromagnetic, antiferromagnetic, and nonmagnetic. Description of thevariety of types of magnetic materials is not made herein in detail.However, let it suffice here to say, that a ferromagnetic material isone in which magnetic moments of atoms within the ferromagnetic materialtend to, on average, align to be both parallel and in the samedirection, resulting in a nonzero net magnetic magnetization of theferromagnetic material.

Most materials like copper, silver, and gold are diamagnetic materials,which do not exhibit a net magnetization. These materials tend topresent an extremely weak magnetization opposite and proportional to anapplied (external) magnetic field. Diamagnetic materials are also callednonmagnetic materials.

An antiferromagnetic material is one in which magnetic moments withinthe antiferromagnetic material tend to, on average, align to beparallel, but in opposite directions, resulting in a zero netmagnetization.

As shown, the conventional prior art GMR element 200 can include a seedlayer 202 disposed over the substrate, an antiferromagnetic pinninglayer 204 disposed over the seed layer 202, and a pinned layer 206disposed over the antiferromagnetic pinning layer 204. The pinned layer206 can be comprised of a first ferromagnetic pinned layer 206 a, asecond ferromagnetic pinned layer 206 c, and a spacer layer 206 bdisposed there between.

The conventional GMR element 200 can also include a spacer layer 208disposed over the second ferromagnetic pinned layer 206 c, and a freelayer 210 disposed over the spacer layer 208. The spacer layer 206 b isa nonmagnetic metallic layer. The spacer 208 is also a nonmagneticlayer, which can be metallic for GMR or insulating for TMR. The freelayer 210 can be comprised of a first ferromagnetic free layer 210 a anda second ferromagnetic free layer 210 b.

A cap layer 212 can be disposed over the free layer 210 to protect theGMR element 200.

Examples of thicknesses of the layers of the conventional prior art GMRelement 200 are shown in nanometers. Examples of materials of the layersof the conventional prior art GMR element are shown by atomic symbols.

Within some layers, arrows are shown that are indicative or directionsof magnetic field directions of the layers when the GMR element 200 doesnot experience an external magnetic field. Arrows coming out of the pageare indicated as dots within circles and arrows going into the page areindicated as crosses within circles.

Taking the layers from the bottom upward, the seed layer 202 is used toprovide a regular crystalline structure upon the substrate that affectscrystal properties of layers above.

With regard to the antiferromagnetic pinning layer 204, sub-layers(i.e., layer portions) within the antiferromagnetic pinning layer 204tend to have magnetic fields that point in alternating differentdirections indicated by right and left arrows, resulting in theantiferromagnetic pinning layer having a net magnetic field of zero. Atop surface of the antiferromagnetic pinning layer 204 tends to have amagnetic moment pointing in one direction, here shown to the left.

With regard to the pinned layer 206, the first ferromagnetic pinnedlayer 206 a tends to couple to the top surface of the antiferromagneticpinning layer 204, and thus, the magnetic field in the firstferromagnetic pinned layer 206 a can by aligned in parallel to themagnetic moments at the top surface of the antiferromagnetic pinninglayer 204, here shown to the left.

Due to the presence of the spacer layer 206 b between the first andsecond ferromagnetic pinned layers 206 a, 206 c the second ferromagneticpinned layer 206 c tends to couple antiferromagnetically with the firstferromagnetic pinned layer 206 a, and thus, it has a magnetic fieldpointing in the other direction, here shown pointing to the right. Thecombination of the three layers 206 a, 206 b, 206 c can be referred toas a synthetic antiferromagnetic structure or layer.

The first and second free layers 210 a, 210 b have respective magneticfields pointing out of the page in the absence of an external magneticfield. This pointing direction can be achieved by creating a specificanisotropy along a direction pointing out of the page. That anisotropycan be created by a shape of the GMR element. For example, theanisotropy can be created by patterning the GMR element 200 (top view)to have a yoke shape, or by a crystalline or a magnetic anisotropy. Ayoke shape is more fully described below in conjunction with FIG. 5. Bycreated the yoke shape, the free layer 210 has a preferential axis (theyoke axis). If the yoke axis is perpendicular to the referencemagnetization a crossed anisotropy can be achieved, which allowsobtaining a linear response on a field extension of the order of thefree layer anisotropy.

In operation, when the conventional GMR element 200 is exposed to anexternal magnetic field pointing in a direction of an arrow 214, themagnetic fields in the ferromagnetic free layers 210 a, 210 b tend torotate to the right to become more aligned (or fully aligned, i.e.,pointing to the right) with the magnetic field pointing direction in thesecond ferromagnetic pinned layer 206 c. However, the magnetic fields inthe pinned layer 206 are pinned by the antiferromagnetic pinning layerand do not rotate. The amount of rotation of the magnetic fields in theferromagnetic free layers 210 a, 210 b depends upon the magnitude of theexternal magnetic field. The increased alignment of the magnetic fieldsin the ferromagnetic free layers 210 a, 210 b with the direction of themagnetic field in the second ferromagnetic pinned layer 206 c tends tomake a resistance of the GMR element 200 lower. In particular,resistance tends to vary primarily in the first free layer 210 a, in thesecond (Cu) spacer layer 208, and in the second ferromagnetic (e.g.,CoFe) pinned layer 206 c.

Conversely, when the GMR element is exposed to an external fieldpointing opposite to the direction of the arrow 214, the magnetic fieldsin the free layer 210 tend to rotate to the left to become moreanti-aligned (or fully anti-aligned, i.e., pointing to the left) withthe magnetic field pointing direction in the second ferromagnetic pinnedlayer 206 c. The amount of rotation depends upon the magnitude of theexternal magnetic field. The increased anti-alignment of the magneticfields in the ferromagnetic free layers 210 a, 210 b with the directionof the magnetic field in the second ferromagnetic pinned layer 206 ctends to make a resistance of the GMR element 200 higher.

In view of the above, it will be understood that, referring briefly toFIG. 1, in the absence of an external magnetic field, a resistance ofthe GMR element 200 is at the center of the linear region 102 a, and theresistance can move to the right or to the left on the transfercharacteristic curve 102 (i.e., lower or higher) depending upon adirection of the external magnetic field 214. When full alignment orfull anti-alignment of layers is achieved, the GMR element 200 will bein the lower saturation region 102 e or the upper saturation region 102d, respectively.

In general, the ferromagnetic free layers 210 a, 210 b tend to naturallyhave a plurality of magnetic domains, including, but not limited to, afirst plurality of magnetic domains with magnetic fields pointing in afirst direction and a second plurality of magnetic domains with magneticfields pointing in one or more other directions. The first plurality ofmagnetic domains in the ferromagnetic free layers 210 a, 210 b havemagnetic field pointing directions that are aligned with the netmagnetic field of the free layer 210, shown to be coming out of the pagewhen the GMR element 200 is not exposed to an external magnetic field,but which can rotate as the GMR element 200 is exposed to a magneticfield. As described above, the magnetic field pointing direction of thefirst plurality of magnetic domains rotates in response to the externalmagnetic field. The second plurality of magnetic domains tends to havemagnetic field pointing directions that point in one or more otherdirections.

Simply stated, with regard to the steps 104 of FIG. 1, each step isgenerated when one or more of the magnetic domains that are not withinthe first plurality of magnetic domains (e.g., that are within thesecond plurality of magnetic domains), i.e., one or more of the magneticdomains with magnetic fields not pointing in the direction of the netmagnetic field in the ferromagnetic free layers 210 a, 210 b, suddenlysnaps (i.e., jumps) in direction to become aligned with the net magneticfield pointing direction of the magnetic field in the ferromagnetic freelayers 210 a, 210 b, wherever the net field in the ferromagnetic freelayers 210 a, 210 b may be pointing (i.e., may have rotated) in responseto an external magnetic field. However, it is also possible that one ormore of the magnetic domains with magnetic fields not pointing in thedirection of the net magnetic field in the ferromagnetic free layers 210a, 210 b more slowly transitions in direction to become aligned with thenet magnetic field pointing direction of the magnetic field in theferromagnetic free layers 210 a, 210 b, in which case one or more of thesteps of FIG. 1 would be less steep than those shown, but stillundesirable. Thus, it would be desirable to reduce a number of magneticdomains in the free layer 210 that point in directions other than thedirection of the net magnetic field in the free layer 210 (i.e., reducethe quantity of magnetic domains within the second plurality of magneticdomains). This reduction would result in fewer steps 104, smaller steps104, or no steps 104.

In order to reduce the number of magnetic domains in the free layer 210that point at directions other than the direction of the net magneticfield of the free layer, i.e., in order to reduce the number of magneticdomains that point in directions other than out of the page, an externalbiasing magnet can be used. As an alternative, a plurality of layers canbe added to the basic GMR element 200 in order to achieve an intra-stackmagnetic bias with a so-called “double pinned” arrangement.

Referring now to FIG. 3, a conventional prior art double pinned GMRelement 300 can include a nonmagnetic seed layer 302, anantiferromagnetic pinning layer 304 disposed over the seed layer 302, apinned layer 306 disposed over the pinning layer 304, a spacer layer 308disposed over the pinned layer 306, and a free layer 310 disposed overthe spacer layer. In some arrangements, the free layer 310 can becomprised of two ferromagnetic free layers 310 a, 310 b. In somearrangements, the spacer layer 308 is a nonmagnetic layer.

The double pinned GMR element 300 can further include a spacer layer 312disposed over the free layer 310, a second pinned layer 314 disposedover the spacer layer 312, a second pinning layer 316 disposed over thesecond pinned layer 314, and a nonmagnetic cap layer 318 disposed overthe second pinning layer 316. In some arrangements, the spacer layer 312is a nonmagnetic layer.

Examples of thicknesses of the layers of the GMR element 300 are shownin nanometers. Examples of materials of the layers of the GMR element300 are shown by atomic symbols.

The prior art double pinned GMR element 300 achieves a magnetostaticfield created by the second pinned layer 314. The second pinned layer314 layer is coupled ferromagnetically to the bottom surface of a secondantiferromagnetic pinning layer 316, and thus, the magnetic field in thesecond pinned layer 314 points in the same direction as the magneticmoments at the bottom surface of the antiferromagnetic pinning layer316, here shown pointing into the page.

The material used for the second antiferromagnetic pinning layer 316 isdifferent from the one used for the first antiferromagnetic pinninglayer 304. In this way the magnetization of the two layers 304, 316 canbe manipulated independently by exploiting different blockingtemperatures of the two materials (below 230° C. for IrMn and well above250° C. for PtMn).

The second pinned layer 314 has a magnetic field oriented, here shown tobe pointing into the page, to be perpendicular to the magnetic field ofthe first pinned layer 306. In particular, the pointing direction of themagnetic field created by the second pinned layer 314 and experienced bythe free layer 310 causes a reduction in the number of magnetic domainsin the free layer 310 that point in directions other than the directionof the net magnetic field of the free layer 310, e.g., a reduction inthe number of magnetic domains that point in directions other than outof the page.

A thickness of the spacer layer 312 is chosen to provide a desiredmagnetic coupling strength between the second pinned layer 314 and thefree layer 310. In some embodiments, the thickness of the Ta of thespacer layer 312 is only a few Angstroms, and the coupling takes placesalso through pinholes in the spacer layer 312. It will be understoodthat a thickness of a deposition of only a few angstroms is difficult tocontrol, and pinhole density is also difficult to control. Thus, theamount of magnetic coupling between the second pinned layer 314 and thefree layer 310 is difficult to control.

For a GMR element, the spacer 308 is a metallic nonmagnetic layer(usually Copper). For a TMR element, the spacer 308 is an insulatingnonmagnetic layer (e.g., Al2O3 or MgO). Otherwise, the GMR element 300can have layers the same as or similar to a comparable TMR element.Thus, a TMR element is not explicitly shown.

Referring now to FIG. 4, an example of a double pinned GMR element 400includes a plurality of layers disposed over a substrate. An uppersurface of the substrate is shown as a dark line at the bottom of FIG.4.

On the left side of FIG. 4, each layer is identified by functional name.On the right side or FIG. 4 are shown magnetic characteristics ofsub-layers that can form the functional layers.

Examples of thicknesses of the layers of the GMR element 400 are shownin nanometers. Examples of materials of the layers of the GMR element400 are shown by atomic symbols.

In general, magnetic materials can have a variety of magneticcharacteristics and can be classified by a variety of terms, including,but not limited to, ferromagnetic, antiferromagnetic, and nonmagnetic.Brief descriptions of these types of magnetic materials are given above.

As shown, the exemplary GMR element 400 can include some of the samelayers described above for the prior art GMR element of FIG. 3. Like theprior art GMR element of FIG. 3, the exemplary GMR element 400 caninclude a seed layer 402 disposed over the substrate, anantiferromagnetic pinning layer 404 disposed over the seed layer 402,and a pinned layer 406 disposed over the antiferromagnetic pinning layer404. However, in some embodiments, the pinned layer 406 can be comprisedof a first ferromagnetic pinned layer 406 a, a second ferromagneticpinned layer 406 c, and a spacer layer 406 b disposed therebetween. Insome embodiments, the spacer layer 406 b is comprised of a nonmagneticmaterial.

In some other embodiments, the pinned layer 406 can instead be comprisedof one pinned layer, the same as or similar to the pinned layer 306 ofFIG. 3.

Due to the presence of the spacer 406 b between the first and secondferromagnetic pinned layers 406 a, 406 c, the second ferromagneticpinned layer 406 c tends to couple antiferromagnetically with the firstferromagnetic pinned layer 406 a, and thus, it has a magnetic fieldpointing in the other direction, here shown pointing to the right. Asdescribed above, the combination of the three layers 406 a, 406 b, 406 ccan be referred to as a synthetic antiferromagnetic structure or layer.

The exemplary GMR element 400 can also include a spacer layer 408disposed over the second ferromagnetic pinned layer 406 c, and a freelayer 410 disposed over the spacer layer 408. In some embodiments, thefree layer 410 can be comprised of a first ferromagnetic free layer 410a disposed under a second ferromagnetic free layer 410 b. In someembodiments, the spacer layer 408 is comprised of a nonmagnetic material(e.g., conductive Cu for GMR or an insulating material for TMR).

Like the prior art GMR element 300 of FIG. 3, the GMR element 400 ofFIG. 4 can further include a spacer layer 412 disposed over the secondferromagnetic free layer 410 b, and a second pinned layer 414 disposedover the spacer layer 412. In some embodiments, the second pinned layer414 can be comprised of a ferromagnetic material. In some embodiments,the spacer layer 412 is comprised of a nonmagnetic material (e.g., Ru)

The GMR element 400 of FIG. 4 can further include a secondantiferromagnetic pinning layer 416 disposed over the second pinnedlayer 414.

A cap layer 418 can be disposed at the top of the GMR element 400 toprotect the GMR element 400.

Within some layers, arrows are shown that are indicative or directionsof magnetic fields of the layers when the GMR element 400 does notexperience an external magnetic field. Arrows coming out of the page areindicated as dots within circles and arrows going into the page areindicated as crosses within circles.

In some embodiments, the seed layer 402 is comprised of Ru or Ta, andthe first antiferromagnetic pinning layer 404 is comprised of PtMn. Insome embodiments, the first pinned layer 406 is comprised of the firstferromagnetic pinned layer 406 a comprised of CoFe, the spacer layer 406b comprised of Ru, and the second ferromagnetic pinned layer 406 ccomprised of CoFe. In some embodiments, the spacer layer 408 iscomprised of Cu (or alternatively, Au, or Ag). In some embodiments, thefirst ferromagnetic free layer 410 a is comprised of CoFe and the secondferromagnetic free layer 410 b is comprised of NiFe. In someembodiments, the spacer layer 412 is comprised of Ru (or alternatively,Au, or Ag), the second pinned layer 414 is comprised of CoFe, the secondantiferromagnetic pinning layer 416 is comprised of PtMn, and the caplayer 418 is comprised of Ta. However, other materials are alsopossible.

The spacer layer 412 being comprised of Ru (or Au, or Ag) allowsrealizable ranges of thicknesses (described below) of the spacer layer412 to allow for partial pinning of the free layer 410. Partial pinningis described more fully below.

In some other embodiments, the first and second antiferromagneticpinning layers 404 and 416 can be comprised of IrMn, FeMn, or any othertype of antiferromagnetic material. PtMn or IrMn are shown in thefigure, and PtMn is used in examples below. In some other embodiments,the second pinned layer 414 can instead be comprised of a plurality ofsublayers, the same as or similar to the sublayers of the first pinnedlayer 406. In some other embodiments, the spacer layer 408 can becomprised of Ta or Cu.

A thickness of the spacer layer 412 is selected to provide a desiredamount of (i.e., a partial) magnetic coupling between the second pinnedlayer 414 and the free layer 410. Also, the thickness of the spacerlayer 412 is selected to provide a desired type of magnetic couplingbetween the second pinned layer 414 and the free layer 410, i.e.,ferromagnetic coupling or antiferromagnetic coupling, or betweenferromagnetic and antiferromagnetic coupling. Here, the coupling isshown to be ferromagnetic coupling, but, by selection of the thicknessof the spacer layer 412, the coupling can be antiferromagnetic orbetween ferromagnetic and antiferromagnetic coupling.

In some embodiments for which the spacer layer 412 is comprised of Ru,the thickness of the spacer layer 412 is selected to be within a rangeof about 0.1 to about 4 nm, but preferably between about 0.9 and 4.0 nmfor robustness of the manufacturing process, i.e., thick enough that thespacer layer 412 can be deposited with repeatable and reliablethickness. In some embodiments, a thickness of the spacer layer 412 isgreater than 0.5 nm, or greater than 0.6, 0.7, 0.8, 0.9, 1.0, or 2.0 nm,i.e., greater than a thickness of the spacer layer 312 of the prior artdouble pinned GMR element 300 of FIG. 3.

Taking CoFe and NiFe to have similar magnetic properties, it will berecognized that the layers of materials above the first ferromagneticfree layer 410 a and below the first ferromagnetic free layer 410 a aresimilar, but in reversed order, namely, NiFe (or CoFe)/Ru/CoFe/PtMn.However, it is desired that the spacer layer 406 b provides highcoupling between surrounding layers, thus it is thin, while it isdesired that the spacer layer 412 provide less coupling betweensurrounding layers, thus it is thicker.

Ru is well suited for the spacer layer 412 because it allowsantiferromagnetic or ferromagnetic coupling (also called Ruderman KittelKasuya Yoshida or RKKY coupling) between surrounding layers, accordingto the Ru thickness. In essence, the Ru material permits couplingthrough it, as opposed to in spite of it. This allows for a thicker Rulayer 412, with a range of achievable thickness values, to achieve andto tune the desired partial pinning of the free layer 410. Partialpinning is more fully described above and below.

In contrast, it should be understood that the Ta spacer layer 312 ofFIG. 3 is only used as a nonmagnetic spacer layer and does not provideRKKY coupling. In essence, the Ta spacer layer 312 only decouples thefree layer 310 from the pinned layer 314. However, as described above,the Ru spacer layer 412 of FIG. 4 provides RKKY coupling between thefree layer 410 and the pinned layer 414.

In some embodiments, the thickness of the Ru spacer layer 412 isselected to provide an RKKY coupling of between about −50 mT and about50 mT. The RKKY coupling tends to be stable with respect to possibleprocess drift, i.e., the amount of coupling tends to remain constant andstable even for a thickness change of about ten percent in the Ru layerdue to manufacturing process variations or the like.

Operation of the layers 402-410 is discussed above in conjunction withsimilar layers in FIGS. 2 and 3.

The second pinned layer 414, having a pinned magnetic field pointingdirection aligned with a pointing direction of the magnetic field in thefree layer 410, tends to cause particular behavior within the free layer410. In particular, the pointing direction of the magnetic field in thesecond pinned layer 414 causes a reduction in the number of magneticdomains in the free layer 410 that point at directions other than thedirection of the net magnetic field of the free layer, i.e., a reductionin the number of magnetic domains that point in directions other thanout of the page when in the presence of no external magnetic field.

As described above in conjunction with FIG. 2, in general, theferromagnetic free layers 410 a, 410 b tend to naturally have aplurality of magnetic domains, including, but not limited to, a firstplurality of magnetic domains with magnetic fields pointing in a firstdirection and a second plurality of magnetic domains with magneticfields pointing in one or more directions different than the firstdirection. The first direction described above can be parallel to upperand lower surfaces of the free layer 410. The first plurality ofmagnetic domains have magnetic field pointing directions that arealigned with the net magnetic field of the free layer 410 shown to becoming out of the page when the GMR element 400 is not exposed to anexternal magnetic field, but which can rotate as the GMR element 400 isexposed to a magnetic field. As described above, the magnetic fieldpointing direction of the first plurality of magnetic domains in thefree layer 410 rotates in response to an external magnetic field, e.g.,420. The second plurality of magnetic domains will tend to have magneticfield pointing directions that point in the one or more directionsdifferent than the first direction.

Also as described above in conjunction with FIG. 2, with regard to thesteps 104 of FIG. 1, each step is generated when one or more of themagnetic domains that are not within the first plurality of magneticdomains (e.g., that are within the second plurality of magneticdomains), i.e., one or more of the magnetic domains with magnetic fieldsnot pointing in the direction of the net magnetic field in the freelayer 410, suddenly snaps (or more slowly rotates) in direction tobecome aligned with the magnetic field pointing direction of the netmagnetic field in the free layer 410, wherever the net magnetic field inthe free layer 410 may be pointing (i.e., may have rotated) in responseto an external magnetic field.

The second pinned layer 414 is operable to partially magneticallycouple, through the spacer layer 412, to the free layer 410, to reduce anumber of magnetic domains (i.e., to reduce a quantity of magneticdomains in the second plurality of magnetic domains) in the free layer410 that point in a direction other than the first direction, i.e.,other than the direction of the net magnetic field in the free layer 410in the absence of an external magnetic field. This reduction results infewer steps 104, smaller steps 104, or no steps 104. The reduction caninclude a reduction in a quantity of magnetic domains within the abovesecond plurality of magnetic domains.

By partial pinning, it is meant that there is less magnetic couplingbetween the second pinned layer 414 and the free layer 410 than betweenthe first pinned layer 406 and the free layer 410. An amount of partialpinning is determined in part by a material and a thickness of thespacer layer 412.

The PtMn first and second antiferromagnetic pinning layer 404, 416 canhave a Neel temperature and a blocking temperature that are both aboveabout three hundred degrees Celsius. This high temperature is importantto eliminate loss of magnetic characteristics of the GMR element 400 inhigh temperature applications, for example, automobile applications.

While the layers of the GMR element are shown in a particular order, itshould be understood that, in other embodiments, the layers 404, 406(i.e., 406 a, 406 b, 406 c), and 408 can be exchanged with the layers416, 414, 412, respectively. In some embodiments, all of the layersshown in FIG. 4, except for the seed layer and the cap layer, can bereversed in order from bottom to top, as shown below in conjunction withFIG. 10.

The coupling strength and hence the anisotropy amplitude is controlledby the nonmagnetic spacer layer 412 between the free layer 410 and thesecond pinned layer 414. In the prior art arrangement of FIG. 3, a verythin Ta spacer 312 is used. In manufacturing, it is difficult to controlthe thickness of the thin Ta spacer 312, and thus, it is difficult tocontrol the amount of magnetic coupling between the second pinned layer314 and the free layer 310 of FIG. 3. In contrast, the arrangement ofFIG. 4 uses a different nonmagnetic spacer layer 412, allowing a strongRKKY coupling between the second pinned layer 414 and the free layer410. Ru, Ag, or Au can be used for the spacer layer 412.

RKKY coupling decreases and switches between a maximum antiferromagneticcoupling and a maximum ferromagnetic coupling as the distance betweenthe pinned layer 414 and the free layer 410 increases (i.e., as thethickness of the nonmagnetic spacer layer 412 is increased). A minima ofcouplings (referred to as a second minimum of coupling) appears betweenthese maxima and occurs at ranges of thicknesses where the coupling canbe tuned by way of selection of the thickness. In some embodiments, amaterial of the spacer layer 412 can be chosen around the second minimumof coupling (e.g., 1.3 nm for Ru), which allows a much more reproducibledeposition process than currently used for the thin Ta spacer 312 ofFIG. 2, which just decreases coupling rapidly with thickness.

For a GMR element, the spacer layer 408 is a metallic nonmagnetic layer(usually Copper). For a TMR element, the spacer layer 408 is aninsulating nonmagnetic layer (e.g., Al2O3 or MgO). Otherwise, the GMRelement 400 can have layers the same as or similar to a comparable TMRelement. Thus, a TMR element is not explicitly shown.

Referring now to FIG. 5, in which like elements of FIG. 4 are shownhaving like reference designations, according to a specific embodiment,the magnetoresistance element 400 of FIG. 4, and also magnetoresistanceelements described below in conjunction with FIGS. 10 and 11, can beformed in the shape of a yoke 500. A section line A-A shows theperspective of FIGS. 4, 10, and 11.

The yoke 500 has a main part 501, two arms 506, 508 coupled to the mainpart 501, and two lateral arms 512, 514 coupled to the two arms 506,508, respectively. In some embodiments, the main part 501, the two arms506, 508, and the two lateral arms 512, 514 each have a width (w).However, in other embodiments, the widths can be different.

A length (L) of the yoke 500 and a length (d) of the lateral arms 512,514 of the yoke 500 are each at least three times the width (w) of theyoke 500, and the width (w) of the yoke 500 can be between about one μmand about twenty μm.

The yoke dimensions can be, for example, within the following ranges:

-   -   the length (L) of the main part 501 of the yoke 500 can be        between about ten μm and ten millimeters;    -   the length (l) of the arms 506, 508 of the yoke 500 can be at        least three times the width (w);    -   the width (w) of the yoke 500 can be between about one μm and        about twenty μm.

The arms 506, 508 of the yoke 500 are linked to the lateral arms 512,514, which are parallel to the main part 501, and have a length 1 whichis between about ¼ and ⅓ of the overall length (L).

In general, sensitivity of the magnetoresistance element 400 having theyoke shape 500 decreases with the width (w), and the low frequency noiseof the magnetoresistance element 400 increases with the width (w).

The yoke shape offers better magnetic homogeneity in a longitudinallycentral area of the main part 501. This is due to the demagnetizingfield of the yoke length which is mainly along the main part 501, andthis induces an anisotropy of the free layer 410 of FIG. 4, which can beseen as a magnetization at zero field along the length of the yoke 500.If the pinned layer (e.g., 406 of FIG. 4) has a magnetic fieldperpendicular to the yoke (e.g., arrow 502), when an external field isapplied in direction of the arrow 502, the free layer 410 magnetizationrotates uniformly, i.e. without domain jumps. The homogeneous rotationof the magnetization of the free layer 410 results in a response curvewithout steps in the response (see, e.g., FIG. 1)

For a GMR element, the overall stack can be designed in a yoke shape,but for a TMR element, in some embodiments, only the free layer can havea yoke shape.

In other embodiments, the GMR or TMR elements 400 is not formed in theshape of a yoke, but is instead formed in the shape of a straight bar,e.g., having the dimensions L and w, and not having features associatedwith the dimensions 1 and d. For the bar shaped GMR or TMR element,still the section line A-A is representative of the cross sections ofthe GMR element 400 of FIG. 4 or the magnetoresistance elements of FIGS.10 and 11.

Referring now to FIG. 6, a magnetic field sensor 600 can include one ormore magnetoresistance elements. Here, four magnetoresistance elements,which can be of a type described above in conjunction with FIG. 4, orbelow in conjunction with FIGS. 10 and 11, are arranged over a commonsubstrate. The four magnetoresistance elements can be arranged in abridge. Other electronic components (not shown), for example, amplifiersand processors, can also be integrated upon the common substrate.

The magnetic field sensor 600 can be disposed proximate to a movingmagnetic object, for example, a ring magnet 602 having alternating northand south magnetic poles. The ring magnet 602 is subject to rotation.

The magnetic field sensor 600 can be configured to generate an outputsignal indicative of at least a speed of rotation of the ring magnet. Insome arrangements, the ring magnet 602 is coupled to a target object,for example, a cam shaft in an engine, and the sensed speed of rotationof the ring magnet 602 is indicative of a speed of rotation of thetarget object.

While the magnetic field sensor 600 is used as a rotation detector, itshould be understood that other similar magnetic field sensors, forexample, current sensors, having one or more the magnetoresistanceelements of FIG. 4, 10, or 11 can also be realized.

It should be appreciated that FIG. 7 shows a flowchart corresponding tothe below contemplated technique that would be implemented withsemiconductor manufacturing equipment. Rectangular elements (typified byelement 704 in FIG. 7), herein denoted “processing blocks,” representprocess steps.

It will be appreciated by those of ordinary skill in the art that,unless otherwise indicated herein, the particular sequence of blocksdescribed is illustrative only and can be varied without departing fromthe spirit of the invention. Thus, unless otherwise stated the blocksdescribed below are unordered meaning that, when possible, the steps canbe performed in any convenient or desirable order.

Referring now to FIG. 7, an exemplary process 700 for manufacturing adouble pinned GMR element as in FIG. 4 above, begins at block 702, wherethe full stack 400 of FIG. 4, or the magnetoresistance elements of FIG.10 or 11 below, is deposited in sequential deposition steps. Thisdeposition can be followed at block 704 by a patterning process. Thepatterning can result, for example, in the yoke shape of FIG. 5.

After the patterning of block 704, a first annealing is applied at block706 to the processed wafer, where the direction of the magnetic field inthe first pinned layer (e.g., 406 of FIG. 4), and also directions in thefirst antiferromagnetic layer (e.g., 404 of FIG. 4) are defined.Typically the annealing is performed at a temperature T1 with a magneticfield H1 applied parallel to the wafer and, for instance, parallel tothe arrow 502 of FIG. 5. This annealing can have, for example, a onehour duration under a magnetic field of 1 T at 295° C., but these valuesare adapted to the stack composition, i.e., layer materials.

After this first annealing of block 706, at block 708, a secondannealing is performed to define the magnetization of the second pinnedlayer (e.g., 414 of FIG. 4) and of the second antiferromagnetic layer(e.g., 416 of FIG. 4), which provides a magnetic field in the secondpinned layer and also in the second antiferromagnetic layer that areoriented perpendicular to the direction of the magnetic field in thefirst pinned layer (e.g., 406 of FIG. 4) and the directions in the firstantiferromagnetic layer (e.g., 404 of FIG. 4). This annealing step canhave, for example, a one hour duration, at a temperature T2, which canbe equal to T1, and with a magnetic field H2 that is lower than themagnetic field H1. The magnetic field H2 can be applied in a directionparallel to the arrow 504 of FIG. 5. This step is meant to orientate themagnetization of the second pinned layer (e.g., 414 of FIG. 4) withoutchanging the magnetization direction and value of the first pinned layer(e.g., 406 of FIG. 4).

Example values and examples of ranges of values are listed below inTable 1 for the double pinned layer arrangement of FIG. 4 having twoPtMn pinning layers 404, 416.

TABLE 1 Value Typical Approximate Range T1 295° C. 260° C. to 320° C. H11T ≥0.3T Duration 1 1 Hour 30 minutes to 2 hours T2 300° C. 180° C. to350° C. H2 80 mT 20 mT to 200 mT Duration 2 1 Hour 30 minutes to 5 hours

Referring now to FIGS. 8 and 9, in which like elements of FIG. 7 areshown having like reference designations, similar processes 800, 900 canbe also applied according to the steps of FIG. 7 but in different ordersas shown.

In all of the processes 700, 800, 900, the magnetic field H2 appliedduring the second annealing is smaller than H1 and applied in anotherdirection, preferably perpendicularly to H1.

Referring now to FIG. 10, in which like elements of FIG. 4 are shownhaving like reference designation, a double pinned GMR element 1000 haslayers 402, 406, 408, 412, 414 and 416 of FIG. 4 but reversed in stackuporder from those described above in conjunction with FIG. 4. While thepinning layer 416 can again be comprised of PtMn, IrMn, FeMn, or anyother type of antiferromagnetic material, PtMn or IrMn are shown in thefigure, and IrMn is used in examples below. (PtMn is used for examplesin conjunction with FIGS. 4 and 7-9).

Unlike the double pinned GMR element 400 of FIG. 4, the above describednonmagnetic layer 412, which provides the above-described desirablecharacteristics for partial pinning, is below rather than above the freelayer 412.

It should be understood that the reversed stackup of the GMR element1000 may be preferred when the pinning layer 416 is comprised of IrMn.For the GMR element 400 of FIG. 4, if IrMn were used for the pinninglayer 416, it would be deposited on top of the CoFe pinned layer 414,which is not desirable. It has been identified that IrMn does not growwell, i.e., with a regular crystalline structure, when grown over a CoFelayer. However, the IrMn layer 416 grows well over the seed layer 402.

In the double pinned GMR elements 400 and 1000 of FIGS. 4 and 10,respectively, it should be appreciated that the layers 406 a, 406 b, 406c form a so-called “synthetic antiferromagnet” (SAF) structure, forwhich the layers 406 a, 406 c are antiferromagnetically coupled (i.e.,have magnetic fields in opposite directions). Thus, the pinned layer 406forms a SAF structure. In contrast, the pinned layer 414 is but a singlelayer.

It has been observed that a SAF structure used as a pinned layer is morestable that a pinned layer formed as a single layer. In particular,under very high temperature storage life (VTSL) conditions with amagnetic field (e.g., 180° C., 0.2 T) a single layer pinned layer tendsto become aligned with or rotate toward a direction of the externalmagnetic field, even after the VTSL conditions are removed, and thus,can rotate from the direction in which it was originally annealed. Theundesirable rotation can result in a less sensitive GMR element, or evenin an insensitive GMR element over parts of its operating characteristiccurve.

In contrast, it has also been observed that a SAF structure used as apinned layer is more stable and tends to rotate less in the presence ofthe same VTSL conditions, and comes back to the original position moreeasily (i.e., reduced hysteresis). To this end, in FIG. 11 describedbelow, the single layer pinned layer 414 of FIGS. 4 and 10 can bereplaced with a SAF structure. Thus, the free layer 410 can besurrounded with two SAF structures used as two pinned layers.

Referring now to FIG. 11, in which like elements of FIGS. 4 and 10 areshown having like reference designations, a double pinned GMR element1100 is like the double pinned GMR element 1000 of FIG. 10, except thesingle layer pinned layer 414 of FIG. 10 is replaced by a SAF structure1102. In some embodiments, the SAF structure 1102 can be comprised of afirst ferromagnetic pinned layer 1102 a, a second ferromagnetic pinnedlayer 1102 c, and a spacer layer 1102 b disposed therebetween. In someembodiments, the spacer layer 1102 b is comprised of a nonmagneticmaterial.

It should be apparent that the free layer 410 is surrounded by pinnedlayers 406, 1102, both of which are SAF structures. Spacer layers 412,408 are disposed between the free layer 410 and the SAF structures 1102,206, respectively.

It should also be apparent that an upper surface of theantiferromagnetic pinning layer 416 has a magnetic field reversed indirection from an upper surface of the pinning layer 416 of FIG. 10.

Spacer layers 406 b, 1102 b (also referred to herein and nonmagneticlayers) within the two SAF structures have a material and a thicknessselected to result in strong antiferromagnetic coupling betweensurrounding ferromagnetic layers 406 a, 406 b and 1102 a, 1102 b.

It has been observed that the double pinned GMR element 1100 has agreater stability with respect to VTSL conditions than the double pinnedGMR element 1000 of FIG. 10 or the double pinned GMR element 400 of FIG.4.

As in the double pinned GMR element 1000 of FIG. 10, the above describednonmagnetic layer 412 that provides the above-described desirablecharacteristics for partial pinning, is below rather than above the freelayer 412. However, in other embodiments, all layers between the caplayer 418 and the seed layer 402 can be reversed in position.

It should be apparent that a reversed stackup of all layers other thanthe seed layer 402 and the cap layer 418 can provide a double pinned GMRelement similar to the double pinned GMR element of FIG. 4, but with thevarious layers reversed and still with the pinned layer 414 of FIG. 4replaced by the SAF structure 1102 of FIG. 11.

While particular layer thicknesses are shown in FIGS. 4, 10, and 11, itwill be understood that the thicknesses of some layers can bemanipulated to provide a more sensitive double pinned GMR element.

Referring briefly to FIG. 7 above, typical values for annealing a doublepinned layer arrangement of FIG. 11 having a PtMn pinning layer 404 anda PtMn pinning layer 416, i.e., two PtMn pinning layers, are shown belowin Table 2.

For Table 2 and for the double pinned GMR element of FIG. 11,temperature T1, magnetic field H1, and duration 1, refer to annealing ofthe PtMn antiferromagnetic layer 404 and of the SAF structure 406.Temperature T2, magnetic field H2, and duration 2, refer to annealing ofthe PtMn antiferromagnetic layer 416 and of the SAF structure 1102.

TABLE 2 Value Typical Approximate Range T1 270° C. 250° C. to 320° C. H11T ≥0.3T Duration 1 1 Hour 30 minutes to 2 hours T2 160° C. 100° C. to350° C. H2 1T 50 mT to 1T Duration 2 1 Hour 30 minutes to 5 hours

Referring again briefly to FIG. 7 above, typical values for annealing adouble pinned layer arrangement of FIGS. 4, 10, and 11 having a PtMnpinning layer 404 and an IrMn pinning layer 416 are shown below in Table3.

For Table 3 and for the double pinned GMR elements of FIGS. 4 and 10,temperature T1, magnetic field H1, and duration 1, refer to annealing ofthe PtMn antiferromagnetic layer 404 and of the pinned layer 406.Temperature T2, magnetic field H2, and duration 2, refer to annealing ofthe IrMn antiferromagnetic layer 416 and of the associated pinned layer414.

For Table 3 and for the double pinned GMR element of FIG. 11,temperature T1, magnetic field H1, and duration 1, refer to annealing ofthe PtMn antiferromagnetic layer 404 and of the pinned (SAF) structure406. Temperature T2, magnetic field H2, and duration 2, refer toannealing of the IrMn antiferromagnetic layer 416 and of the pinned(SAF) structure 1102.

TABLE 3 Value Typical Approximate Range T1 295° C. 280° C. to 320° C. H11T ≥0.3T Duration 1 1 Hour 30 minutes to 2 hours T2 160° C. 100° C. to260° C. H2 1T 50 mT to 2 T Duration 2 30 minutes 10 minutes to 2 hours

While double pinned GMR elements are described above, it should beunderstood that the double pinned arrangements can be part of astructure with additional pinning and/or pinned layers.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent that other embodimentsincorporating these concepts, structures and techniques may be used.Accordingly, it is submitted that that scope of the patent should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

What is claimed is:
 1. A magnetoresistance element deposited upon asubstrate, comprising: a stack of layers disposed upon a substrate, thestack of layers comprising: a first antiferromagnetic pinning layerdisposed over the substrate; a second antiferromagnetic pinning layerdisposed over the substrate; a first synthetic antiferromagnet (SAF)structure disposed proximate to the first antiferromagnetic pinninglayer; and a second synthetic antiferromagnet (SAF) structure disposedproximate to the second antiferromagnetic pinning layer, wherein thefirst and second synthetic antiferromagnet (SAF) structures are disposedbetween the first and second antiferromagnetic pinning layers, whereinthe first and second antiferromagnetic pinning layers have differentthicknesses.
 2. The magnetoresistance element of claim 1, wherein thefirst and second antiferromagnetic pinning layers are both comprised ofPtMn.
 3. The magnetoresistance element of claim 2, wherein a thicknessof the first antiferromagnetic pinning layer is in a first range of fiveto fifteen nanometers and the second antiferromagnetic pinning layer isa second range of fifteen to thirty nanometers.
 4. The magnetoresistanceelement of claim 2, wherein the magnetoresistance element has a yokeshape.
 5. The magnetoresistance element of claim 4, wherein a length (L)of the yoke shape and a length (d) of lateral arms of the yoke shape areeach at least three times a width (w) of the yoke shape, and the width(w) of the yoke shape is between about one μm and about twenty whereinthe length (L) is a longest dimension of the yoke shape.
 6. Themagnetoresistance element of claim 2, wherein the magnetoresistanceelement comprises a spin valve.
 7. The magnetoresistance element ofclaim 2, wherein the magnetoresistance element comprises a GMR sensingelement.
 8. The magnetoresistance element of claim 2, wherein themagnetoresistance element comprises a TMR sensing element.
 9. Themagnetoresistance element of claim 2, wherein magnetic field directionsin the first and second antiferromagnetic layers are annealed indifferent directions.
 10. A method of fabricating a magnetoresistanceelement, comprising: depositing the magnetoresistance element in a stackof layers upon a substrate, the stack of layers comprising: a firstantiferromagnetic pinning layer disposed over the substrate; a secondantiferromagnetic pinning layer disposed over the substrate; a firstsynthetic antiferromagnet (SAF) structure disposed proximate to thefirst antiferromagnetic pinning layer; and a second syntheticantiferromagnet (SAF) structure disposed proximate to the secondantiferromagnetic pinning layer, wherein the first and second syntheticantiferromagnet (SAF) structures are disposed between the first andsecond antiferromagnetic pinning layers, wherein the first and secondantiferromagnetic pinning layers have different thicknesses.
 11. Themethod of claim 10, wherein the first and second antiferromagneticpinning layers are both comprised of PtMn.
 12. The method of claim 11,wherein a thickness of the first antiferromagnetic pinning layer is in afirst range of five to fifteen nanometers and the secondantiferromagnetic pinning layer is a second range of fifteen to thirtynanometers.
 13. The method of claim 11, wherein the magnetoresistanceelement has a yoke shape.
 14. The method of claim 13, wherein a length(L) of the yoke shape and a length (d) of lateral arms of the yoke shapeare each at least three times a width (w) of the yoke shape, and thewidth (w) of the yoke shape is between about one μm and about twenty μm,wherein the length (L) is a longest dimension of the yoke shape.
 15. Themethod of claim 11, wherein the magnetoresistance element comprises aspin valve.
 16. The method of claim 11, wherein the magnetoresistanceelement comprises a GMR sensing element.
 17. The method of claim 11,wherein the magnetoresistance element comprises a TMR sensing element.18. The method of claim 11, further comprising: annealing magnetic fielddirections in the first and second antiferromagnetic layers to be indifferent directions.
 19. The method of claim 11, further comprising:annealing the first synthetic antiferromagnet (SAF) structure and thefirst antiferromagnetic structure at a first annealing temperature, witha first annealing magnetic field, with a first annealing magnetic fielddirection, and with a first annealing duration; and annealing the secondsynthetic antiferromagnet (SAF) structure and the secondantiferromagnetic structure at a second annealing temperature, with asecond annealing magnetic field, with a second annealing magnetic fielddirection, and with a second annealing duration, wherein: the firstannealing magnetic field direction is in a selected magnetizationdirection, the second annealing magnetic field direction is in adifferent direction than the first annealing magnetic field direction,and the first annealing magnetic field is higher than the secondannealing magnetic field, wherein the second annealing magnetic field isselected to result in annealing of the second synthetic antiferromagnet(SAF) structure and annealing of the second antiferromagnetic structurewithout affecting the annealing of the first synthetic antiferromagnet(SAF) structure or the annealing of the first antiferromagneticstructure.
 20. The method of claim 19, wherein the first annealingmagnetic field is about one Tesla, and wherein the second annealingmagnetic field is about one Tesla.
 21. The method of claim 20, whereinthe first annealing temperature is about two hundred ninety five degreesCelsius, wherein the second annealing temperature is about one hundredsixty degrees Celsius, and wherein the first annealing duration is aboutone hour and the second annealing duration is about one hour.